Fort de Dailly, Military fortress in canton Vaud, Switzerland

Fort de Dailly is an underground fortress in the mountains east of the Saint-Maurice valley with tunnels, artillery positions, and machinery rooms. The installation is built into the rock of Massif de Dailly and spreads across several levels of defense infrastructure.

Construction began in 1892, and Savatan and Dailly were handed over to the troops at the end of 1894. In the night of 28 May 1946, three ammunition magazines holding 449 tonnes exploded, killing ten workers; the fort was rebuilt from 1948. The last modernization followed in 1990, and the artillery works were abandoned in 1995.

This fortress represents Swiss military engineering and shows the defensive technology of its era. Visitors can see how soldiers worked within the preserved chambers and passages to protect the region.

Visits are through guided tours offered from April onwards, providing access to underground passages and machinery rooms. It is wise to wear warm clothing as the temperature underground stays cool, and bring sturdy shoes for uneven surfaces.

An internal funicular system connects this fortress with Fort de Savatan, allowing soldiers to move quickly between strategic positions. This transport system was unusually innovative for coordinated defense of the region.